A wireless communication device operates in a wireless communication system to provide a user of the device with portable communications. A wireless communication device communicates with the wireless communication system or other wireless communication devices via electromagnetic signals, such as those in the radio frequency (RF) range, for example. The wireless communication device may communicate voice only, data only or both voice and data. The format of the electromagnetic signal communicated between the wireless communication device and the wireless communication system or other devices may be either analog or digital. Examples of wireless communication devices comprise radiotelephones, pagers, one-way radios, two-way radios, personal data assistants, and personal notebooks. The radiotelephones comprise cellular and cordless subscriber units. A cellular radiotelephone system forming the wireless communication system, for example, is described in EIA/TIA INTERIM STANDARD, Cellular System Dual-Mode Mobile Station-Base Station Compatibility Standard, IS-54-B, Telecommunications Industry Association, April 92.
Wireless communication devices use various alert techniques to indicate to a user of a wireless communication device that an incoming desired signal has been received. For example, a radiotelephone alerts the user when an incoming call signal is received, and a pager alerts the user when an incoming page signal is received. Generally, these alert techniques include audible, visual and tactile alert generators. The audible alert generator is typically implemented with an acoustic transducer, i.e. a speaker, sometimes known as a ringer. The visual alert generator is typically implemented with a display or a separate indicator. The tactile alert generator is typically implemented with an axially offset counter-weight driven by a motor to cause a vibrating sensation.
Audible alert generators are generally known in virtually all wireless communication devices. When a desired signal has been received, the wireless communication device activates the audible alert generator to produce a sound, such as a ring or beep, thereby alerting the user. A problem with audible alert generators is that the sound produced can be disturbing to others in environments where there is a low ambient noise level, and may not be heard by the user in environments where there is a high ambient noise level.
Visual alert generators are generally known in most wireless communication devices. When a desired signal has been received, the wireless communication device activates the visual alert generator to produce a visual indicator, such as a flashing icon in the display or a flashing light, thereby alerting the user. A problem with visual alert generators is that the visual indicator produced can go undetected by the user for some period of time until the user actually looks at the visual indicator. Therefore, the audible alert generator is typically used as a primary alert and the visual alert generator is typically used as a secondary or redundant alert.
Tactile alert generators are generally known in only some wireless communication devices. Tactile alert generators are typically used in wireless communication devices that are small enough to be portable and worn on the user such that the tactile sensation is felt. Some pagers and radiotelephones, for example, have the motor driving the axially offset counter-weight to produce a vibrating sensation against the user. When a desired signal has been received, the wireless communication device activates the tactile alert generator to produce a tactile sensation, such as vibration, thereby alerting the user. A problem with tactile alert generators is that the tactile sensation produced can go undetected by the user when the wireless communication device is not worn by the user or closely coupled to the user in some manner. Therefore, the tactile alert generator is typically used in environments where the ambient noise level is very low such that others in the area are not disturbed or environments where the ambient noise level very high such that the user is alerted when the audible alert cannot be heard.
U.S. Pat. No. 4,918,438 discloses a paging receiver for receiving a paging signal. When the paging signal is received, the paging receiver drives one of a tactile and audible alert for a first predetermined period of time, and automatically drives the other alert for a second period of time on lapse of the first predetermined period of time. Therefore, the paging receiver drives the alerts automatically and sequentially regardless of whether the paging receiver is on the user. However, operating this paging receiver independent of its location relative to the user has disadvantages. First, if the paging receiver drives the tactile alert before the audible alert and the paging receiver is not on the user, the user is not alerted until the audible alert is generated during the second predetermined period of time. In a radiotelephone application, a calling party or the radiotelephone system may terminate a call during the first predetermined period of time before the paging receiver drives audible alert. Second, if the paging receiver drives the audible alert before the tactile alert, the audible alert may disturb others is in a quiet environment.
U.S. Pat. No. 5,189,389 discloses a paging receiver having an alert mode sensor for determining when the paging receiver is on and off a user. When the paging receiver activates a first alerting device when the paging receiver is determined to be on the user and activates a second alerting device when the paging receiver is determined to be off the user. The alert mode sensor senses the position of a belt clip on the paging receiver or the position of the paging receiver in a battery charger.
A motion sensor for a pager, disclosed in Motorola Technical Publication, volume 14, page 60, December 1991, causes a silent (e.g. vibrator) alert device to be activated when motion of the pager is detected and causes an audible alert device to be activated when no motion of the pager is detected.
A capacitance sensor or an infrared sensor for a radiotelephone handset, disclosed in Motorola Technical Publication, volume 12, pages 102-103, April 1991, determines the location of the radiotelephone handset relative to a user and controls circuitry in the radiotelephone handset responsive to the determined location.
Other types of proximity sensors include eddy-current sensors, variable reluctance sensors, Hall-effect sensors, reed switch sensors, reflective optical sensors, metal detecting sensors, and microwave sensors.
The eddy-current sensors are limited to applications that rely on a very large change in field disturbance to kill an oscillator. A killed oscillator circuit requires a large change in reactance. Therefore, the size of a detected object needs to be large thereby yielding a coarse resolution system.
The variable reluctance sensors, are typically used to sense a toothed or binarily arranged, metallic wheel for sensing rotary position or speed.
Hall-effect sensors detect a change in a polarity of a magnetic field. Therefore, a target is limited to a magnetic material. Hall-effect sensors are sensitive to a gap between the target and the sensor and typically have a limited temperature operating range.
Reed switch sensors detect a change in a magnetic field. Therefore, a target is limited to a magnetic material.
Reflective optical sensors are generally fragile, are limited to a medium temperature range, have a medium resolution, and need a relatively clean environment to operate reliably.
Metal detecting sensors typically detect a shift in an oscillator frequency. They are typically used to detect large targets introduced into a radiating field based on a change in inductance attributable to permitivity, or permeability due to a permeable target intruding this field. This type of sensor technology requires a relatively large target needed to significantly shift the oscillator frequency.
Microwave sensors include those that work on a Doppler shift principle and those that work on a gross change in reactance. The Doppler shift type sensors are normally used to measure the speed of a passing object. Although they may be adapted in a one or two-state encoders they are relatively more expensive and complex than other, simpler approaches. The second type of microwave based sensors looks for a major change in an oscillator's reactive field by introducing a reactive target within the field thereby killing or starting the oscillator. This scheme is typically limited to sensing large changes in reactance.
Accordingly, there is a need for a wireless communication device having an electromagnetic wave proximity sensor which overcomes the disadvantages of the prior art.